Ashraf Hassan Farha

Morphological and Structural Properties of NbN Thin Films Deposited by Pulsed Laser Deposition

Niobium nitride (NbN) films were deposited on Nb using pulsed laser deposition (PLD), and the effect of substrate deposition temperature on the preferred orientation, phase, and surface properties of NbN films were explored by x-ray diffraction (XRD) and atomic force microscopy (AFM). It was found that the substrate deposition temperature has a significant influence on properties of the NbN films, leading to a pronounced change in the preferred orientation of the crystal structure and the phase. We find that substrate temperature is a critical factor in determining the phase of the NbN films. For a substrate temperature of 650 °C 850 °C, the NbN film formed in the cubic δ-NbN phase mixed with the β-Nb2N hexagonal phase. With an increase in substrate temperature, NbN layers became β-Nb2N single phase. Essentially, films with a mainly β-Nb2N hexagonal phase were obtained at deposition temperatures above 850 °C. Surface roughness and crystallite sizes of the β-Nb2N hexagonal phase increased as the deposition temperatures increased.

Pulsed laser deposition of niobium nitride thin films

Niobium nitride (NbNx) films were grown on Nb and Si(100) substrates using pulsed laser deposition. NbNx films were deposited on Nb substrates using PLD with a Q-switched Nd:YAG laser (λ = 1064 nm, ∼40 ns pulse width, and 10 Hz repetition rate) at different laser fluences, nitrogen background pressures and deposition substrate temperatures. When all the fabrication parameters are fixed, except for the laser fluence, the surface roughness, nitrogen content, and grain size increase with increasing laser fluence. Increasing nitrogen background pressure leads to a change in the phase structure of the NbNx films from mixed β-Nb2N and cubic δ-NbN phases to single hexagonal β-Nb2N. The substrate temperature affects the preferred orientation of the crystal structure. The structural and electronic, properties of NbNx deposited on Si(100) were also investigated. The NbNx films exhibited a cubic δ-NbN with a strong (111) orientation. A correlation between surface morphology, electronic, and superconducting propertie...

Generation of Plasma Plume From Ge Target by Nanosecond Laser

Properties of the plasma plume in pulsed-laser deposition affect the quality of the deposited film. We show images of laser-produced plasma upon the ablation of a germanium target by a nanosecond laser and compare the shapes of plume at different nitrogen background pressures. Understanding the mechanism of laser-produced plasma is critical to control the quality of the deposited film.